"Syndrome creates the 'killbot' that learns the moves of every super-human." But this killbot turns on him, suggesting that machines and inanimate objects are trying to get rid of their biggest threat, aka humans.

"The monsters' civilization is actually Earth in the incredibly distant future... It’s possible that the monsters are simply the personified animals mutated after the diseased earth was radiated for 800 years."

The monsters have an energy crisis, which is supplied by the humans... by way of time travel.